Upload the gh file so we can all talk about the same thing. If your gh file also depends on curves defined in a 3dm file, then either include the 3dm file as well or internalise the curves.

Is the current use of fields in that file an attempt at achieving the effect you’re after, or is it something that needs to stay in place while the additional deformation logic is added?

Yes, you can adjust the amount of deformation by multiplying each motion vector with a scalar (a number in between zero and one ideally). If you multiply by zero it means the motion vector shrinks to zero, thus yielding no motion. You can generate these scalars by projecting the grid points to a linear space such as a line.